A Case of Bardet-Biedl Syndrome Etemadi K1, Khazaii MR2 1. MSC of Human Genetic, Molecular Medicine and Genetic department, Medical school, Hamadan University of medical sciences. 2. Assistant professor of Pediatric Urology Abstract Background: The Bardet Biedl syndrome is a heterogenous and autosomal recessive disorder. Primary features are: retinitis pigmentosa, obesity, polydactyly, mental retardation, renal abnormalities and hypogonadism. Renal failure is the major cause of death in homozygote patients, with chronic glomerolopathy that cause chronic renal disease. Secondary features are: speech disorder delay, developmental delay, polyuria, diabetes mellitus and hypertension. The diagnosis of Bardet- Biedl syndrome is established by clinical findings. Twelve genes are known to be associated with Bardet Biedl syndromes: BBS1, BBS2… BBS12. Case presentation: In this article we report a four and half year old boy that have Bardet Biedl syndrome as a result of a consanguine marriage (third degree). Conclusion: A monogenic syndrome such as Bardet Biedl has a lot of symptoms. These symptoms are out put of a mutation in locus of a recessive allel. Therefore people like to marry consanguinly have to do genetic counseling before marriage. Because analysis of family history will reduced the risk of such syndromes. Key words: Bardet Biedl Syndrome